The present invention generally relates to a method for producing an olefin polymer or copolymer of high stereospecificity at a high rate of yield, while controlling the polymer's molecular weight distribution, when applied to polymerization or copolymerization of .alpha.-olefin having three or more carbon atoms.
In general, the olefin polymer produced with a MgCl.sub.2 supported catalyst has a narrow distribution of molecular weights. Many efforts have been made to broaden the distribution of molecular weights, so as to improve at the time of processing the flow characteristics of the product produced by this catalyst. For this, a method has been in wide use, in which polymers of different distributions of molecular weights are first made by the use of a plurality of polymerization reactors and later mixed, but this has disadvantages in that it requires much time and effort and the product is often found to be very uneven. In a recent report, from Mitsui Petrochemical of Japan (publication No. 93-665, of Korean Patent), a method has been proposed in which an olefin polymer with a wider distribution of molecular weights is produced by the use of two particular electron donors, from which homopolyolefin's having a melt flow rate (MFR) ratio greater than 31.6 are respectively polymerized in the same polymerization conditions. In this case, however, the catalyst's activity is reduced too low for it to be commercially useful, and not merely is its molecular weight distribution difficult to control, but the catalyst's reactivity with hydrogen, which controls the molecular weight distribution of the polymer, is so low as to pose many limitations on the management of its processing.
Meanwhile, many other techniques are known to produce polymers or copolymers of high stereospecificity by the use of solid complex titanium catalysts containing magnesium with electron donors, and also titanium and a halogen, as catalyst for polymerization or copolymerization of .alpha.-olefin which contains more than three atoms of carbon (e.g. Japanese. Pts. Laid-Open Nos. 73-16986 and 73-16987, Ger. Pts. Laid-Open No.2,153,520; 2,230,672; 2,230,-728; 2,230,752; and 2,553,104).
These references reveal the use of mixture components of particular catalysts and the process for forming these catalysts. As is well known, the characteristics of these catalysts, containing solid complex titanium, vary from catalyst to catalyst, accordant with the different mixtures of components, different combinations of processes for formation, and the different combinations of these conditions. Therefore, it is very difficult to predict what effects can be obtained from a catalyst produced under a given set of conditions. Often, a catalyst having undesirable effects is produced. It is also often true that such characteristics as the activity of the catalyst or the stereospecificity of the polymer do not turn out to be adequate even if the catalyst is made under proper conditions, if proper external electron donors are not used.
The solid complex titanium catalyst containing magnesium, titanium, and halogen is no exception. In polymerizing or copolymerizing .alpha.-olefin containing more than three atoms of carbon, in the presence of hydrogen and with the use of a catalyst composed of titanium and an organometallic compound of metals belonging to Groups I through IV on the periodic table of elements, if a co-catalyst composed of titanium trichloride obtained by reducing titanium tetrachloride using metallic aluminum, hydrogen, or an organic aluminum compound is used, along with such electron donors as are known to restrain the formation of amorphous copolymer, the effects vary, depending upon the electron donors used. The cause is accepted to be that the electron donors are not mere inert additives, rather, they combine with the magnesium and titanium compounds electronically and sterically, thereby fundamentally altering the structure of the solid complex catalyst.
New methods for creating polymers of higher yields than the existing methods, by the use of certain silicone compounds, have been developed by Dow Corning of the U.S. (U.S. Pat. No. 5,175,332 and EP Laid-Open No. 602,922), Mitsui Petrochemical of Japan (Korean Pat. Pub. Nos. 92-2488 and 93-665; U.S. Pat. No. 4,990,479; EP Laid-Open No. 350,170; Canadian Pat. No. 1,040,379), and well-known European makers.